Your confidence and interest!
If you feel confident with your abilities to train as for the dedication and desire to learn and grow in the process, I would say go for it.
I say this as you are working with a horse that you have been riding already. Just as the horse learns, you learn too and together. This is just my opinion though, and I have nothing against trainers as they are important.
I have been working with horses for just over a decade, but there is always one I may get that will throw me for a loop! LOL! I love the satisfaction of learning together with a new horse, and developing. I like challenges too, which is why they are my interest! From the BLM projects to a 10 year old unbroke brood mare, theres always satisfaction making it happen. Then there is working with the babies, and doingshow work. I always get to finish the day with something new learned!
Dixon's Red Hot Ember